1. Field of the Invention
The present invention relates to an actuator unit that shifts a door lock device of a vehicle between a locked position and an unlocked position.
This application claims priority from Japanese Patent Application No. 2006-153783, filed Jun. 1, 2006, which is incorporated herein by reference in its entirety.
2. Description of the Related Art
An actuator unit for shifting a door lock device of a vehicle between a locked position and an unlocked position is described, for example, in Japanese Patent No. 3310965. The actuator unit includes an electric motor that includes a worm gear fixed to its drive shaft, a worm wheel that engages with the worm gear, an output shaft that is parallel to an axis of the worm wheel, and a transmission mechanism that transmits rotation of the worm wheel to the output shaft. A driving force of the electric motor counter-turns the output shaft between a first angular position and a second angular position to shift the door lock device between the locked position and the unlocked position. The actuator unit includes as the transmission mechanism a drive gear mounted on the worm wheel, and a rotating lever mounted on the output shaft. Drive gear teeth mesh with rotating lever teeth, as required, to transmit rotation of the worm wheel to the output shaft.
In the actuator unit, the transmission mechanism is configured such that when the drive gear is placed in a predetermined neutral angular position, the drive gear does not rotate even when the rotating lever is oscillated. Specifically, the actuator unit is configured in such a manner that when the drive gear is in the neutral angular position due to shifting of the drive gear teeth in the axial direction of the worm wheel, the rotating lever teeth do not engage with the drive gear teeth by the oscillation of the rotating lever. On the other hand, when the drive gear rotates, the drive gear teeth engage with the rotating lever teeth. Thus, the conventional actuator unit does not cause any extra burden of operation when the door lock device is shifted between the locked and unlocked positions manually, and operability of the actuator unit is not compromised.
In the conventional actuator unit, after the output shaft is rotated due to the rotation of the worm wheel either in the first position or in the second position, position of the worm wheel needs to be specified so that the drive gear is always in the neutral angular position. Therefore, in the conventional actuator unit, a return spring is arranged within a case that houses the worm wheel for restoring the worm wheel in the neutral angular position by the resilience of the return spring after the electric motor is stopped.
However, in the conventional actuator unit with such configuration, the return spring is always elastically deformed when the output shaft is rotated. Thus, a larger electric motor is needed to resist the elasticity of the return spring, which is not desirable when downsizing of the actuator unit is required.